1. Field of the Invention
The invention generally relates to wireless signal call handling and specifically the handling of wireless calls among base stations (BS).
2. Description of the Related Art
Wireless communication networks are currently experiencing wide popularity in the form of cellular communication systems. Wireless communication networks typically comprise a plurality of base stations that connect wireless subscribers to other communication system users. A base station services a wireless subscriber by providing a communication link over a radio channel for a call, such as, for example, a telephone call. The base station then communicates information and/or voice signals associated with the call, or call signals, to further networks, which may include the public switched telephone network (PSTN). In general, such systems include a central control processor (xe2x80x9cCCPxe2x80x9d) that is connected to and coordinates the operations of the plurality of base stations. In cellular systems, the CCP is sometimes referred to as the executive cellular processor.
Ordinarily, a particular base station can only service a wireless subscriber who is located in close enough proximity to have sufficient radio signal strength to sustain the call. Accordingly, wireless networks employ several base stations which are situated in different geographical areas such that a user is typically within close enough proximity to at least one of the base stations. Cellular systems, for example, operate in this manner. One of the primary features of a cellular system is the ability to provide uninterrupted service to a call while the subscriber is actively moving in and out of the vicinity of several base stations. In such systems, when the subscriber moves to a location in which the radio signal strength weakens or otherwise deteriorates, the system causes another more suitably located base station to service the call. The system effects the base station change using a procedure referred to as a handoff procedure.
Because wireless communication systems are currently experiencing substantial popularity, the number of users is increasing. The growing user population can create congestion of the frequency spectrum presently allocated for wireless communications. As a result there has been a need to utilize the available frequency spectrum in a more efficient manner. There are several methods by which wireless systems exploit the limited available frequency spectrum in order to maximize the call traffic capacity. These methods feature call signal modulation techniques, including time division multiple access (TDMA) and code division multiple access (CDMA) modulation techniques. Of these, the use of CDMA provides several advantages over the other techniques because it allows the frequency bands within the spectrum to be reused by several subscribers simultaneously. This frequency reuse further increases system capacity.
Another advantage of the frequency reuse capabilities of CDMA wireless systems is that it enables the use of a soft handoff procedure. A soft handoff is a procedure in which a second base station is added to service a call while the original base station continues to service the call. In such cases, both base stations communicate concurrently with the subscriber. Upstream network connections may then utilize signals from the base station having the better connection to the subscriber. For example, consider a call that is serviced by a first base station. Ordinarily, the first base station communicates with the subscriber and forwards the subscriber""s call signals to and from an upstream telephone network. If a soft handoff is executed and a second base station is added to service the call, both the first and second base stations would then communicate with the subscriber. Furthermore, the upstream network connection would then select signals from either the first or second base station to forward to the upstream network. Typically, the better of the two signals is forwarded.
In systems using base station controlled handoffs, a base station servicing the call, often called the primary base station, is responsible for making handoff decisions. Base station controlled handoffs not only reduce the computational load on the system""s CCP, but also reduce delay in the handoff procedure by reducing communications between the base station and the CCP. Such systems have been described in, for example, M. J. English, et al. U.S. Pat. No. 5,305,308 that issued Apr. 19, 1994, at column 36, line 1 to column 37, line 6.
During normal wireless call handling, in a wireless network using CDMA soft handoff techniques, it is standard for base stations to send back to the controlling base station, a list of radio resources (cells) that are near each of the cells that currently provide radio contact with the mobile station. In other words, base stations typically send xe2x80x9cneighbor listsxe2x80x9d, so that a base station not only includes information of its neighboring base stations, but also of base stations neighboring its neighboring base stations.
With the increased use of data applications, call holding times increase and the possibility exists that a mobile station (MS) will move beyond the geographical area known to the BS that is controlling the call. In this case, the controlling BS must request radio resources to complete a soft handoff to a neighboring base station. But as the mobile station in a call with a long holding time continues to move beyond the range of even its neighboring base stations, the controlling BS must request radio resources from other BSs that it may not normally communicate with, such as neighbors of its neighbors, and for which it does not know the correct signaling address. Use of the main switching station and slow signal handoff between base stations could cause a call to be dropped. Accordingly, a need exists for controlling base stations to communicate directly with neighboring base stations and to have access to information for communicating with neighbors of its base station neighbors.
The controlling base stations, in order to support the longer holding times of calls, must be able to access the resources of the neighbors of its neighbors, and even their neighbors as the mobile station moves farther and farther away from the point where the call began. These neighbors of neighbors, and neighbors of neighbors of neighbors can be referred to as second order neighbors, third order neighbors, etc. The controlling base station, in order to access resources of its immediate, or first order neighbors, must be able to communicate with those neighbors to request those resources. Thus, a need exists for enabling controlling base stations to communicate directly with other base stations.
The present invention provides a method and apparatus for base station control signal handoff, permitting base stations to communicate directly with each other. Signaling addresses and identities of further neighbor base stations are provided so that, in effect, a base station is able to communicate directly with neighbors of its neighboring base stations. In this way, the wireless network automatically includes base station identity and address information, thus allowing the controlling base station to communicate directly with any base station necessary to continue support of a call, without the need to communicate through the mobile switching center, and with minimal human intervention.